Method and apparatus for manufacturing integrally finned tubing



March 23, 1965 SAYU KOYAMA ETAL 3,174,319

METHOD AND APPARATUS FOR MANUFACTURING INTEGRALLY FINNED TUBING 2 She ets-Sheet 1- Filed Jan. 5, 1962 (Nu/Ira M00797! March 23, 1965 SAYU KOYAMA ETAL 3,

METHOD AND APPARATUS FOR MANUFACTURING INTEGRALLY F INNED TUBING Filed Jan. 5, 1962 2 Sheets-Sheet 2 Jumw/ /1/04 [aw/1m Mm: y4n4 United States Patent 3,174,319 IWETHOD AND APPARATUS FOR MANUFACTUR- ING INTEGRALLY FINNED TUBING Sayu Koyama, Funabashi-shi, Chiba, Juichi Shida, Shinjuku-ku, Tokyo, and Kunihiro Nakayama, Funabashishi, Chiba, Japan, assignors to Nihon Kentetsu Company Limited, Tokyo, Japan, a corporation of Japan Filed Jan. 5, 1962, Ser. No. 164,528 4 Claims. (Cl. 72-96) The present invention relates to a process for the manufacture of fin tubes for heat exchangers, wherein tube stock is subjected to a rolling operation to reduce both the diameter and the wall thickness thereof so as to produce thereon a continuous spiral fin formed integral with the tube wall; as well as to a machine for carrying out the process.

The main object of the invention is to provide an improved technique for the manufacture of the fin tube of the kind above referred to, wherein the product may be provided with a wider cooling fin than attainable by the conventional technique, yet in a simpler and easier manner.

A further object is to provide an improved technique for the production of fin tubes, having a wide cooling fin, yet having a superior quality in its strength, thus providing a higher mechanical strength of the fin, thereby improving the heat exchange performance of a heat exchanger equipped with such improved fin tubes.

Various further and more specific objects, features and advantages of the invention will appear from the descrip tion given below, taken in connection with the accompanying drawings illustrating by way of example a preferred embodiment of this invention.

In the drawings:

FIG. 1 is a side view of a machine designed for carrying out the novel process according to the present invention, part of which is illustrated in section in order to show the inner detail construction of the machine;

FIG. 2 is a cross-section taken on the line IIII in FIG. 1;

FIG. 3 is a diagrammatic longitudinal section through a forming roll, a mandrel cooperating therewith and a rolling stock placed therebetween, especially illustrative of three fabrication stages of the novel process; and

FIGS. 4 and 5 are explanatory diagrams, illustrating the optimum rolling conditions in the novel process.

Now, referring to the accompanying drawings, a preferred machine designed for carrying out the novel process according to the invention shall be first described more in detail hereinbelow:

In the present machine, three sets of forming roll units, each being denoted generally by reference numeral 1, are provided and arranged substantially in parallel to each other and spaced at equal angular distance from each other, as most clearly seen from FIGS. 1 and 2. Each of said units 1 comprises a rolling shaft or roll proper E, providing three forming sections A, B and C, as diagrammatically shown in FIG. 3. The first forming section A comprises a number of forming discs a having a selected thickness and mounted fixedly on said rolling shaft E, yet separated one from another by a predetermined distance b. These forming discs a have different outside diameters gradually increasing when seen from right to left in FIG. 1. In order to keep the predetermined gap between each two successive forming discs, spacer means such as a separator ring as shown is provided.

In the similar way, the second section B arranged in continuation of the section A comprises a different number of spaced forming discs 0 having a predetermined wall thickness as before and at a separating gap d one "ice after another. The outside diameters of these discs 0 increase successively rather in an abrupt manner as clearly seen from FIG. 1. Finally, and in the similar manner, the third section C comprises a still different number of forming discs e having a predetermined wall thickness and spaced at a gap distance 1'' one after another equally to fulfil the simultaneous angular adjustment of the three forming shafts E, thus keeping them at a predetermined angular relationship with each other, a stand D appearing at the right hand end of FIG. 1, and a bearing frame D arranged for supporting the bearing means rotatably mounting the right hand ends of said shafts E, are arranged relatively turnable to each other through the intermediary of a circular shoulder connection as at k. The bearing frame D is provided with an adjusting member D for each shaft bearing assembly K thus giving possibility for adjusting the latter radially as desired towards or remote from a tube stock 3 mounted on the working part 4 of the centrally arranged mandrel. For this radial adjustment, there is provided an adjusting screw G for each adjusting member D The opposite end of each forming shaft E is mounted in a bearing K which is in turn supported within a bearing frame D.-,, the latter being adjustably mounted on a similar stand D as before. The frame D may be adjusted by means of an adjusting screw G in the radial direction so as to move the related forming shaft end towards or remote from the tube stock as before, and as occasion may desire. These main bearings K and K may be preferably self-centering roller bearings as shown. The three forming shafts E should be naturally displaced longitudinally to establish an offphase relationship with each other one third the spiral pitch of the product. For this longitudinal adjustment, there is provided an adjusting screw G for each forming shaft, which is, in operation, rotated through the intermediary of a universal joint F from a driving means not shown.

FIG. 2 illustrates the adjustable connection between the bearing frame D and the mounting stand D so as to provide the possibility for pivotally adjusting the forming shafts E. There are three elongated, curved slots D formed in the bearing frame D A set screw G loosely passes through each of these slots and is threaded into the stand D By this adjusting mechanism, all of the forming shafts E are twistingly adjustable relative to the tube stock, as explained hereinbefore. The thus adjusted position of these shafts are naturally set by tightening the screws G FIG. 3 is illustrative of the working mode of the above mentioned forming machine. The mandrel proper (2) has a largest diameter portion g, which corresponds to the inside diameter of the tube stock 3 to be produced. In continuation with the said part g, a relatively considerably tapered portion h and a reduced cylindrical part i, the latter corresponding in its outside diameter to the inside diameter of the fin tube to be produced. This working tool 2 is formed with the slightly reduced stem 4 of the mandrel as shown in FIG. 3. This mandrel is turnably mounted at the center of the forming shaft arrangement as already described. Outside the mandrel stem 4, there is provided heating means 5. Upon operation of the machine, the stock 3 is advanced along the mandrel upon having been heated in the heating means 5.

The thus advanced stock is then squeezed between-the forming roll assemblies and the mandrel while acted upon by the rotating assembly, which is kept in rotation by the driving means as already described. In this way, the forming discs a drive into the outside peripheral surface of the tube stock, thereby producing a spiral groove, while the relieved metal rising up into the gap spaces of the forming discs. The heating temperature of the stock while advancing through the heater may be 50-200 C. in the case of aluminium; and 350-450 C. for silver, by way of example. Heating means 5 may utilize electric resistance heating, flame heating, high frequency induction heating or the like.

The thus produced spiral groove will increase in its depth with further advancement of the rolling stock and at the same time the continuous fin will become higher and higher in its height. When the stock further advances and passes through the second forming section B, it is subjected to a considerable reduction in its diameter and a rather abrupt increase in its thickness and height,'because of the gradual, yet rather increasing diameters of the related forming discs cooperating with the tapered zone hof the mandrel. The stock then passes through the third forming section 0 and is subjected to a finish working so as to produce the finally finished spiral fin having the desired wall thickness as well as the desired spiral pitch.

Briefly, the rolling stock supported on the mandrel is subjected to a rolling action from outside by a number of forming discs in the first processing section A so as to form in the outside surface of the stock a continuous groove of a rather shallow depth, while advancing through the said section, and at the same time relieved material is pressed out into the gap spaces between the forming discs to form a continuous fin having a predetermined outside diameter. The stock is then subjected to a considerable, yet continuous reduction in its diameter, while passing through the second processing section {B, by the second group of processing discs having increasing-peripheral diameters, while thereby increasing correspondingly the Wall thickness of theshaped fin. In this respect, it will be noted that the final outside diameter of-the produced fin at the end of the first processing stage *plays a very important role. More specifically, assuming that the final fin height produced in this stage to be H as shown in FIG. 4, the outside diameter of the fin would be caused to decrease during the reducing stage in the second processing section B, provided that the height H be rather small. In this respect, proper selection of the height H and suitable selection of rigidity in the initially finished fin in consideration of the rigidity of the tube wall having a thickness T at the end of this processing stage should be adopted for avoiding the above mentioned reducing effect upon the initial fin. When the above condition be satisfied, an additional height H will be added during the second processing stage to the preceding initial height H,-thus providing a sum H-l-H as shown in the same'figure. V

The rolling operation is liable to produce longitudinal elongation in the processed stock. According to the conventional technique, such elongation was prevented by the forming discs themselves. Such processing method gave however rise to considerable residual stresses in the finished products, on the one hand, and tended to invite frequent breakage of the forming discs because of considerable longitudinal pressure acting thereupon, on the other hand. On the contrary, according to the present invention, such difficulties may be substantially obviated in that during the same rotational movement of the extremities A and C of the rolls 1, for example by an angle 0 as shown in FIG. 5, the corresponding parts of the stock 3' and 3" are caused to rotate through angles 0' and 0", respectively, so that a certain degree of twisting is imparted to the stock, thus effectively preventing the otherwise possible longitudinal elongation in the stock.

When fabricated according to the novel teachings of this invention, therolling stock and the rolled-out fins thereon are subjected to substantially none of adverselyaffecting residual stresses, thus:the frequently-met POSSI- bility, of cracking and degrading effects are completely avoided. By the final or third processing, the products are finished treated to improve their appearance.

It will be understood that modifications and Variations of the embodiment of the invention disclosed herein may be resorted to without departing from the scope of the concepts of the present invention. Therefore, the scope of the invention should be limited only by the scope and proper interpretation of the claims appended hereto.

What we claim as new and desire to protect by Letters Patent is:

1. In a machine for the manufacture of fin tubes for heat exchangers, the combination comprising a mandrel adapted to support tube stock to be formed into fin tubes,

said mandrel comprising (a) a portion of largest diameter adjacent to the tube entrance end of said machine, said largest diameter being substantially equal to the inside diameter of said tube stock,

(b) an intermediate portion having a relatively steep taper of gradually reduced diameters and (c) a smallest diameter corresponding to the inner diameter of said fin tube to be produced,

a plurality of forming roll assemblies each of said roll assemblies comprising (A) a first section having a plurality of forming disks of substantially equal predetermined thickness, and means separating each two adjacent disks by a substantially equal predetermined distance, the disks of said first section having a gradually increasing outside diameter,

(B) asecond section having a series of forming disks substantially equally spaced as those of section (A) but having abruptly increasing outside diameters,

(C) and a third section having a further series of forming disks substantially equally spaced as those of section (A) but having diameters substantially equal to the largest diameter of section (B), and

(D) a roll shaft on which said three series of disks are mounted,

means for rotatably mounting said plurality of forming rolls symmetrically about said mandrel so that the several series (A) of the assemblies generally surround portion (a) of said mandrel, the second series (B) of the assemblies generally surround portion (b) of said mandrel and the several series (C) of said assemblies generally suurround portion (0) of said mandrel.

2.'The machine as claimed in claim 1, comprising a first set of bearing means adapted to rotatably support one end of each of said roll assemblies,

2. second set of bearing means adapted to rotatably support the other end of each of said supporting rolls, frame means to retain said bearing means,

means to adjust the position of at least one pair of the first and second sets of bearings in an axial direction.

3. The machine as claimed in claim 2, comprising means to adjust the sets of bearings in said frame to change the axial inclination thereof with respect to the axis of said mandrel.

4. In the process for the manufacture of fin tubes for heat exchangers, the steps comprising,

mounting tube stock on a rotatable mandrel having a large diameter portion at one end, a small diameter portion at the other end and an intermediate portion of gradually decreasing diameter from the large POI-I .tion to the small portion,

advancing said stock from the large end of the mandrel toward the short end thereof,

applying rolling pressure to said tube stock from at least two symmetrically arranged series of substantially equally spaced forming disks as the tube stock passes along said mandrel to produce thereon spiral ridges in the spaces between adjacent disks of said forming disks,

said forming disks substantially matching and approaching the surface of said mandrel in the three defined portions of said mandrel whereby said radiating fins are being formed as the internal diameter of said tube stock is being reduced.

References Cited by the Examiner UNITED STATES PATENTS 432,463 7/90 White 8013 5 2,337,490 12/43 Penner 29--l.57.3 2,429,491 10/47 Schuler 80133 2,761,336 9/56 Green et al. 8062 2,983,168 5/61 Laban 8062 10 CHARLES W. LANHAM, Primary Examiner.

WILLIAM J. STEPHENSON, LEON PEAR, Examiners. 

1. IN A MACHINE FOR THE MANUFACTURE OF FIN TUBES FOR HEAT EXCHANGERS, THE COMBINATION COMPRISING A MANDREL ADAPTED TO SUPPORT TUBE STOCK TO BE FORMED INTO FIN TUBES, SAID MANDREL COMPRISING (A) A PORTION OF LARGEST DIAMETER ADJACENT TO THE TUBE ENTRANCE END OF SAID MACHINE, SAID LARGEST DIAMETER BEING SUBSTANTIALLY EQUAL TO THE INSIDE DIAMETER OF SAID TUBE STOCK, (B) AN INTERMEDIATE PORTION HAVING A RELATIVELY STEEP TAPER OF GRADUALLY REDUCED DIAMETERS AND (C) A SMALLEST DIAMETER CORRESPONDING TO THE INNER DIAMETER OF SAID FIN TUBE TO BE PRODUCED, A PLURALITY OF FORMING ROLL ASSEMBLIES EACH OF SAID ROLL ASSEMBLIES COMPRISING (A) A FIRST SECTION HAVING A PLURALITY OF FORMING DISKS OF SUBSTANTIALLY EQUL PREDETERMINED THICKNESS, AND MEANS SEPARATING EACH TWO ADJACENT DISKS BY A SUBSTANTIALLY EQUAL PREDETERMINED DISTANCE, THE DISKS OF SAID FIRST SECTION HAVING A GRADUALLY INCREASING OUTSIDE DIAMETER, (B) A SECOND SECTION HAVING A SERIES OF FORMING DISKS SUBSTANTIALLY EQUALLY SPACED AS THOSE OF SECTION (A) BUT HAING ABRUPTLY INCREASING OUTSIDE DIAMETERS, (C) AND A THIRD SECTION HAVING A FURTHER SERIES OF FORMING DISKS SUBSTANTIALLY EQUALLY SPACED AS THOSE OF SECTION (A) BUT HAVING DIAMETERS SUBSTANTIALLY EQUAL TO THE LARGEST DIAMETER OF SECTION (B), AND (D) A ROLL SHAFT ON WHICH SAID THREE SERIES OF DISKS ARE MOUNTED, MEANS FOR ROTATABLY MOUNTING SAID PLURALITY OF FORMING ROLLS SYMMETRICALLY ABOUT SAID MANDREL SO THAT THE SEVERAL SERIES (A) OF THE ASSEMBLIES GENERALLY THE SURROUND PORTION (A) OF SAID MANDREL, THE SECOND
 4. IN THE PROCESS FOR THE MANUFACTURE OF FIN TUBES FOR HEAT EXCHANGERS, THE STEPS COMPRISING, MOUNTING TUBE STOCK ON A ROTATALY MANDREL HAVING A LARGE DIAMETER PORTION AT ONE END, A SMALL DIAMETER PORTION AT THE OTHER END AND AN INTERMEDATE PORTION OF GRADUALLY DECREASING DIAMETER FROM THE LARGE PORTION TO THE SMALL PORTION, ADVANCING SAID STOCK FROM THE LARGE END OF THE MANDREL TOWARD THE SHORT END THEREOF, APPLYING ROLLING PRESSURE TO SAID TUBE STOCK FROM AT LEAST TWO SYMMETRICALLY ARRANGED SERIES OF SUBSTANTIALLY EQUALLY SPACED FORMING DISKS AS THE TUBE STOCK PASSES ALONG SAID MANDREL TO PRODUCE THEREON SPIRAL RIDGES IN THE SPACES BETWEEN ADJACENT DISKS OF SAID FORMING DISKS, SAID FORMING DISKS SUBSTANTIALLY MATCHING AND APPROACHING THE SURFACE OF SAID MANDREL IN THE THREE DEFINED PORTIONS OF SAID MANDREL WHEREBY SAID RADIATING FINS ARE BEING FORMED AS THE INTERNAL DIAMETER OF SAID TUBE STOCK IS BEING REDUCED. 